Prefer empty items to null ones

There are many cases in which an "empty" object can be used instead of a null object reference. This is usually preferable, since it helps eliminate one of the most common problems encountered during development: the NullPointerException.

The following qualify as "empty" objects:

Example declarations of empty items:

String item = "";
BigDecimal[] items = new BigDecimal[0];
List<Integer> items = new ArrayList<>();
Map<String, Integer> items = new LinkedHashMap<>();

The Collections class contains several type safe methods which return empty items (which are also immutable and Serializable) :

The above methods are occasionally useful.


Here's an example of using an empty, zero-length array instead of a null reference. This simplifies the caller, since they never have to check for null values. (An even better alternative is to use replace the array with a possibly-empty collection.)

import java.util.*;

public final class StockPortfolio {


  * A field is implemented internally as a Collection,
  * but offered to the user of this class as an Array.
  * This array is never null, even if the underlying Collection is
  * empty.
  public String[] getStocks() {
    NO_STOCKS plays a double role here. If there are elements in fStocks, then
    toArray will allocate a new array, using NO_STOCKS simply as an indicator
    of the proper type to use. If fStocks has no elements at all, then toArray
    will simply return the NO_STOCKS array itself.
    return (String[]) fStocks.toArray(NO_STOCKS);


  /** The underlying collection. */
  private List fStocks;

  /** A constant, empty array, to be used instead of a null array. */
  private static final String[] NO_STOCKS = new String[0];

See Also :
Prefer Collections over older classes
Avoid null if possible
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